Process of casting with mold stool protection plate



A ril 28, 1970 w. T. RAWLES PROCESS OF CASTING WITH- MOLD STOOL PROTECTION PLATE Filed Oct. 16, 1967 INVENTOR //////AW 7. FflA ZZ'S 88m; & Semme ATTORNEYS United States Patent O 3,508,600 PROCESS OF CASTING WITH MOLD STOOL PROTECTION PLATE William T. Rawles, P.O. Box 3267, Greeneville, Tenn. 37743 Filed Oct. 16, 1967, Ser. No. 675,397 Int. Cl. B22d 7/12 U.S. Cl. 164-121 8 Claims ABSTRACT OF THE DISCLOSURE The disclosure may be described as process and product for the preservation of stools which are used in connection with the casting of high melting point materials, for example, in the casting of steel in a mold supported by a stool. More specifically, thedisclosure resides in the placement of a tablet or disc, having a higher melting point than the materials which are to be cast, so that as the molten material is poured into the mold upon the stool, the stool shall thereby resist erosion and/or sequential cracking. The objective is thus to preserve the life of the stool indefinitely, the disc having great resistance to thermal shock.

PRIOR ART Although present methods of casting are satisfactory, an expensive portion of the process in the casting of steel resides in the necessity for frequent replacement of the base or stool upon which the mold rests while being filled from the ladle. The present process and product are directed to the preservation of the life of the stool by novel means, exceeding the present concept of spraying a sodium sulfate or other thermal shock resistant substance. Such known methods of spraying the stool are expensive, inefiicient and totally unsatisfactory as to application and removal in preserving the life of the stool. There has also been applied a colloidal silica to the stool to prevent undue erosion from the thermal shock or impact of the steel upon the comparatively cold stool, all without effect.

Another of the principal problems herein resides in the necessity for creating a relatively pure casting from the mold without contamination of casting by protective coatings on the stool. It is believed that the present method meets this objective, an especial attempt being successfully made hereby to absorb the thermal shock of the molten substance as a column is poured into the mold upon the stool. An effort is made herein to provide a means not only to absorb the thermal shock, but as well to prevent the additive from adhering to the ingot, per se.

SUMMARY OF THE INVENTION It will be appreciated that the present process is adapted to the expendable application of a thermal shock. resistant substance to the stool, to preclude erosion and/or cracking of said stool by an insulating quality, as well as by a thermal shock resistant quality.

DESCRIPTION OF THE DRAWINGS FIGURE 1 is an isometric view of the application of the circular thermal shock resistant plate to a stool, revealing in fragment the interposed adhesive;

FIGURE 2 is a sectional view of mold and stool, sche matically showing the pouring of a column of steel at the target area on to the thermal shock resistant plate;

FIGURE 3 is a vieW in vertical section showing a portion of the stool and ingot wherein the shock resistant plate is transformed;

FIGURE 4 is an isometric view showing an ingot in fragment, following cooling and in which the shock resistant plate and adhesive are dispersed pneumatically.

N 3,508,600 Patented Apr- 1970 DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present process, numerous materials may be used to create a satisfactory disc or plate which incidentally is preferably circular in design. But it has been noted. that among the preferred forms is that of a fused silica (pure silica dioxide), the same being known to have the highest resistance to thermal shock of related ceramic's such as cristobalite, or Pyro Ceram (cordicrite) or hepidalite (mineral beta-spodumene) or graphite in its various forms. The melting point of silica dioxide or any of the other materials is believed sufliciently high with respect to the metal being cast to resist erosion and/ or cracking. In practice, it has been found that by the adding. of small amounts of colloidal silica to the silica dioxide in the formation of the plate herein, a reasonable amount of green strength is given to the plate, retarding cracking during its transformation from the pure silica dioxide to cristobalite in the process described hereinafter.

In this process, a satisfactroy fused silica plate is slip cast in pure form, portions of colloidal silica being added where required.

Ingredients:

(A) Colloidal silica (B) Pure silicadioxide (C) Water Another suitable mixture is:

(A) Fused silica (B) Cristobalite (C) Water For the casting of steel ingots, a fused silica circular plate which is molded between 18 and 24" in diameter, thick is satisfactory to accomplish the function. Oft times this plate is cast from a pure silica dioxide having a grain range of 50 to 100 mesh whereupon it is, after being cast in a plaster mold, placed in a kiln under standard slip casting procedure and cured. Colloidal silica may have been added, as aforesaid.

Before covering the selected portion of the stool 100 with the preformed fused silica plate 110, a suitable stool binder 120 is applied to the plate, said binder preferably being in the form of a sodium silicate-silica dioxide mixture (see FIG. 1). By way of example, it is satisfactory to include sodium silicate in the range of 10% and silica dioxide in the range of in powder form in the presence of water.

Water is removed from this mixture sufliciently to form a paste which may be applied to one surface of the fused silica disc or plate. In steel casting, most stools are maintained at a temperature of around 500 F., sufiicient to enhance the setting of the sodium silicate herein and consequentially the present plate to fix it on the stool 100 in the target area of the column of molten steel 140 as it may be poured in the mold (see FIG. 2). In practice, the plate is of sufficient diameter to receive the impact of molten metal should it be slightly offset from the center of the target area, thus insuring that the thermal shock is effectively absorbed. Its circular form and size is such as to insure protection against predictable ladle spout wear and consequent column enlargement.

Upon casting, the fused silica plate 110 transforms from pure fused silica to cristobalite (see FIG. 3), maintaining in effect its original disposition on the stool as the mold may be removed therefrom. The sodium silicate binder having been reduced to a powder by the ingot casting may be easily removed therefrom by pneumatic (or fluid) pressure and the process continued from time to time or from cast to cast (see FIG. 4).

I claim:

1. In the casting of high melting point metals and the like, whereby ladle, mold and stool components are used in the formation of an ingot, the steps of:

(a) providing the stool with a relatively flat upper contacting surface within the mold;

(b) disposing a heat resistant adhesive binder on at least a portion of the contacting surface of the stool;

(c) covering by adhesive contact at least a portion of the contacted surface of the stool with an expendable, high melting point ceramic plate, having resistance to thermal shock and a higher melting point than the metal which is to be cast, whereby at least aportion of said stool normally receiving thermal shock from the flow of the molten metal, may be insulated to protect said stool against erosion and heat cracking;

(d) sequentially pouring a high melting point metal from said ladle onto at least a portion of said ceramic plate, whereby the said plate is modified through heat and time and at least partially disintegrated and said binder is reduced to a powder;

(e) cooling the ingot;

(f) thereafter removing the partially disintegrated plate from the stool and ingot by forcible ejection.

2. The system according to claim 1 in which the plate is fused silica.

3. The process of claim 1 in which the plate comprises a mixture of fused silica and colloidal silica.

4. The process according to claim 3 in which the ratio of colloidal silica to fused silica is approximately 10 to 90.

5. The system according to claim 1 in which the plate is (pyro-ceram) cordicrite.

6. The process according to claim 1 in which the binder is a sodium silicate, the setting of which is enhanced by the pre-heating effect of the stool.

7. The process according to claim 6 in which the binder comprises proportionately at least 10% sodium silicate with the remainder of silica dioxide and in which the mixture may include water, sufiicient to form an amorphous mass.

8. The process of claim 1 in which the plate defines a circular target area upon the stool.

References Cited UNITED STATES PATENTS 3,184,813 5/1965 OShea l64138 X FOREIGN PATENTS 20,3 83 1892 Great Britain.

' 1,060,692. 11/1953 France.

ROBERT D. BALDWIN, Primary Examiner I US. Cl. X.R. 

